CN102020766A discloses a method for preparing flame-retardant copolymerized and modified polyester, in which flame retardant such as 2-carboxyethyl phenyl phosphinic acid or hydroxymethyl phenyl phosphinic acid is added to a mixed slurry of terephthalic acid and ethylene glycol such that the flame retardant and ethylene glycol are subjected to an esterification reaction to obtain flame-retardant polyester repeating units, and that the flame-retardant polyester repeating units and ester obtained by esterification of terephthalic acid with ethylene glycol are subjected to a block copolymerization reaction to obtain the flame-retardant copolymerized and modified polyester.
U.S. Pat. No. 5,399,428 discloses a process for producing a flame-retardant linear polyester. In the process, a polyester prepolymer is obtained by, for example, subjecting ethylene glycol and terephthalic acid to a reaction. The polyester prepolymer and a carboxy-phosphinic acid monomer (for example, 2-carboxyethyl phenyl phosphinic acid) are then subjected to a condensation reaction.
CN1563141A discloses a method for producing phosphorus-based flame retardant polyester in which 2-carboxyethyl phenyl phosphinic acid and ethylene glycol are subjected to an esterification reaction to obtain an intermediate, i.e., ethylene glycol propanoyl ethylene glycol phenylphosphate having a formula of
the intermediate is mixed with 2-carboxyethyl phenyl phosphinic acid and ethylene glycol to obtain a flame retardant mixture, and the flame retardant mixture is added to ester obtained by esterification of terephthalic acid with ethylene glycol to perform a polycondensation reaction.
However, the flame-retardant polyesters obtain by the aforesaid prior art have shortcomings such as inferior stability and significant phosphorus loss.